On Monday, authorities will resume searching the river as well as 60 to 70 acres near the marina as they try to find Ashley Gleeson, 5.

"Obviously, we are hoping for the safe return of Ashley," said Chief Tim Henson of the Dwight Police Department. "However, we want to be sure no stone goes unturned."

It wasn't known how long the boy had been dead, authorities said.

Joshua's body was found in the waters of the Big Basin Marina, located next to the Interstate Highway 55 bridge that spans the Des Plaines River about 50 miles southwest of Chicago.

Officials said Joshua and Ashley were last known to be with their father, Smith's ex-boyfriend Patrick Gleeson, on Nov. 25 and were supposed to be returned to Smith after a weekend visitation.

The children were never returned. On Dec. 7, Gleeson was arrested in Daytona Beach, Fla., in the slaying of his most recent girlfriend, Dena Fuglseth, 43. Her body was found Nov. 29 in the basement of the home they shared in Ottawa County, Mich.

After his arrest, Gleeson, 48, talked with police about some aspects of his case but refused to say anything about the whereabouts of his children.

That has been one of the most frustrating parts of the investigation, Henson said Sunday.

"The only hope we've had is that Mr. Gleeson would do the right thing and come forward" to help police locate his children, he said.

The marina was sealed off as a team of dogs and crime scene investigators began to search the muddy, trash-strewn area, said Illinois State Police Capt. Dan Roach.

Officials from the Department of Natural Resources and a state police airplane were brought in to help with a wider search throughout the river and wooded areas that surround the marina.

"We're not only looking possibly for another victim, but other evidence as well," Roach said.

Even before the body was identified as Joshua's, investigators immediately thought it could be the boy's "because of several coincidences of information that we've known about in the case," Roach said. He did not elaborate.

Investigators aren't sure if Joshua's body was dumped in the waters at the marina or further upriver, Roach said.

Smith and Gleeson, a former factory manager, used to live together in Gardener, Ill. But in June 2001 the couple separated, and Smith got custody of their children and moved to Dwight, 75 miles southwest of Chicago.

Gleeson moved to western Michigan and was granted weekend visitation rights.

Henson said Gleeson was known as a loving father, and nothing seemed unusual when he and Fuglseth traveled to Dwight on Nov. 22 to pick up Joshua and Ashley for what had become a typical weekend visit.

But Gleeson called Nov. 25 to ask for a few more hours with the kids, a request Smith refused because she wanted her daughter to keep up her perfect school attendance.

Smith said she talked with her children by phone that day. And Gleeson said he would return them, but he never did.

A warrant for murder and child abduction was issued for his arrest after Fuglseth's body was found.

Gleeson was arrested after a tow-truck driver in Daytona Beach recognized Gleeson's mini-van from public alerts. He is being held in a jail in Ottawa County.